Fluids returned to surface after well drilling are a mixture of fluids used in drilling along with well cuttings and downhole fluids. The drilling wastes may include lime, emulsifiers, filler, salts, hydrocarbons, formation particulates and water. The particulates may include surface soil and fragments of any rock that the well penetrated. Fluids returned to surface after drilling are processed upon their return to surface to recover expensive components, and the remainder must be disposed of. For example, treatment of the returned fluids may include processing in a shaker to remove larger particulates (shaker cuttings) followed by processing in a centrifuge to remove smaller particulates (centrifuge cuttings). Once the cuttings have been removed, the remaining fluid is recycled for re-use downhole. Shaker cuttings may represent 50-75% of the whole separated cuttings, while centrifuge cuttings may comprise 25% to 50%. The cuttings, once separated from the drilling fluid, are combined in open storage tanks. In a single well that is 2.5 km deep, about 180 m3 of cuttings is produced.
The combined cuttings are referred to as drilling waste. The drilling waste is typically black with a strong hydrocarbon odor, and is a sloppy, sticky, stony mass with a density of 1.5-1.8 g/ml that typically exhibits leaching behavior. The drilling waste is conventionally disposed of by such methods as bio-remediation, stabilization followed by land filling, thermal desorption and thermal treatment. These disposal methods have a tendency towards expense or ongoing environmental hazard. This invention is directed towards an environmentally friendly and economical method of disposing of drilling wastes.
Accordingly, there is provided according to an aspect of the invention, a method for remediation of drilling waste, where the drilling waste is converted to a solid fuel that is environmentally friendly for storage, transportation and combustion. The solid fuel presents no longer danger to the surrounding area and groundwater and has an economical energy value. Using several treatment stages, residual emulsifiers in the drilling waste are chemically in an acidic milieu destabilized and the soil is turned accessible to the hydrocarbons. By using for example a polyelectrolyte in aqueous slurry the hydrocarbon molecules are coagulated and, under normal conditions, irreversibly homogenously adsorbed on the soil particles. Finally, separation and dewatering of the solid fuel can be easily accomplished. The process secures immobilization of the hydrocarbons and no loss in BTU value of the original drilling waste. The BTU value of the converted fuel can be increased by separation of large particulates from the aqueous slurry before immobilization of the hydrocarbons. After rinsing the separated particulates with water, the particulates become free of hydrocarbons and can be left onsite.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.